1. Field of the Invention
The present invention relates to a technology for measuring fuel density in the interior of a combustion chamber of an engine (an internal combustion engine). More specifically, the present invention relates to an apparatus for and method of measuring fuel density in air-fuel mixture supplied to the combustion chambers of an engine.
2. Description of the Related Art
For example, Japanese Laid-open Patent publication No. 11-51866 discloses an apparatus for measuring fuel density in the interior of a combustion chamber, by passing a measuring beam of light of a specific wavelength, which is selectively absorbed by the fuel, through a measuring passage provided in the interior of the combustion chamber, and receiving the measuring beam of light at a light receiving element, to detect the intensity of the received beam of light.
In the described apparatus, the intensity of the measuring beam of light before transmitting through the measuring passage and the intensity of the beam of light after having passed through the measuring passage are introduced in a known logical equation on absorption extinction to perform the calculation of the fuel density.
Nevertheless, even at the timing of measuring the fuel density conducted prior to the start of combustion, there are various kinds of thermal radiations within the combustion chamber of an engine. Thus, the thermal radiations might include radiant light having wavelength identical with that of the measuring light for measuring the fuel density. Therefore, if such radiant light is received by the light receiving element, it is impossible to accurately detect the intensity of the measuring light after having passed through the combustion chamber, which corresponds to the fuel density to be measured. Accordingly, accurate measurement of the fuel density or the air-fuel ratio in the air-fuel mixture cannot be achieved.
In the case where an intensity of light is measured, in order to remove any adverse influence given by background noise, a method is known, in which the light guided to a detector is subjected to chopping at a constant cycle. However, if this method is applied to the measuring of the fuel density, in order to accurately remove the influence by thermal radiation within combustion chambers, which momently varies in response to a change in a crank angle position, the cycle for the chopping must be extremely made short. Thus, it is impossible to adopt this method for measuring fuel density in an engine.